Compressors or fluid-compressing devices are used in various sectors of industry for various applications where compression of fluids, especially (process) gases, is required.
Known examples of this are turbocompressors in mobile industrial applications, such as in exhaust turbochargers or in jet motors, or in stationary industrial applications, such as geared compressors or geared turbocompressors for air separation.
With such a turbocompressor—which operates in a continuous operating mode—the increase in the pressure (compression) of the fluid is brought about by increasing an angular momentum of the fluid from the inlet to the outlet by means of a rotating turbocompressor impeller having radially extending blades and carried by a compressor rotor, by rotation of the blades. Here, i.e. in such a compressor stage, the pressure and temperature of the fluid increase, while the relative (flow) velocity of the fluid in the impeller or turbo impeller falls.
In order to achieve a pressure increase or compression of the fluid which is as high as possible, a plurality of such compressor stages can be arranged in series.
Among the designs of turbocompressor, a distinction is drawn between radial and axial compressors. In the case of the axial compressor, the fluid to be compressed, e.g. a process gas, e.g. air or carbon dioxide, flows through the compressor in a direction parallel to the axis (axial direction). In the case of the radial compressor, the gas flows axially into the impeller of the compressor stage and is then deflected outward (radially, radial direction). In the case of multistage radial compressors, a flow deflection is required after each stage.
Combined designs of axial and radial compressors draw in large volume flows by means of their axial stages, these being compressed to high pressures in the following radial stages.
Whereas single-shaft machines (single-shaft turbocompressors) with a (pinion) shaft carrying one or more impellers—also referred to below for short as a compressor rotor unit—are generally used, the individual compressor stages in (multistage) geared turbocompressors (also referred to below for short as geared compressors) are grouped around a gear, wherein, in this case, a plurality of parallel (pinion) shafts, which each carry one or two impellers (turbo impellers arranged at free shaft ends of the pinion shafts)—accommodated in pressure-resistant spiral housings implemented as housing attachments and allowing flow to and from the compressor stages—as a compressor rotor unit, also referred to below for short as a compressor rotor—are driven by a large driving gearwheel mounted in the housing, a gear.
In the pressure-resistant spiral housing, i.e. in a cylindrical bore in the spiral housing, a spiral insert is inserted—in addition to the impeller or compressor rotor carried by the pinion shaft—in such a way that, axially at the end, the spiral insert still has available to it, in the cylindrical bore of the spiral housing, a spacing enclosed by the spiral housing and the spiral insert, referred to as an annular space, via which the fluid—coming from the impeller—flows out radially via a widening cross section.
Via system piping, such as a pressure stub pipe arranged on the spiral housing or on the (housing) pot and having a pressure stub flange arranged thereon, the fluid then flows onward from the annular space and out of the compressor stage.
The fluid flows into the spiral housing via a spiral intake flange, which is designed as a housing cover (situated axially at the end) and which closes off the spiral housing axially.
A geared compressor of this kind, a geared compressor produced by Siemens designated STC-GC or STC-GV, which is used for air separation, is known from http://www.energy.siemens.com/hq/de/verdichtung-expansion-ventilation/turboverdichter/getriebeturboverdichter/stc-gc.htm or http://www.energy.siemens.com/hq/de/verdichtung-expansion-ventilation/turboverdichter/getriebeturboverdichter/stc-gv.htm (accessed on Dec. 18, 2012).
Assembled rotors for radial compressors are known from US 2011/262284 A1 and U.S. Pat. No. 3,680,979A1 respectively.
To avoid/reduce pressure losses in the compressor stage and/or to prevent (possibly dangerous) process gas from flowing out of the compressor stage (leakage), the pinion shaft carrying the impeller, or compressor rotor, of a turbocompressor of this kind requires a seal between the process gas (in the interior of the compressor stage) to be compressed and an external environment, and said seal must meet different requirements, depending on the type of process gas and the pressure of the process gas (sealing pressure).
One known practice for such sealing is to use seals, such as labyrinth seals or gas seals, arranged on the pinion shaft, which have seal elements that rotate with the pinion shaft and/or do not rotate/are fixed.
Labyrinth seals and gas seals, either in single or double form, are sufficiently well known.
Specifically in the case of compressor rotor designs with overhanging impeller masses or overhung impellers, such as particularly in the case of geared compressors, centering with as little play as possible of all the components which co-rotate—with the compressor rotors—is implemented in order to reduce loads due to unbalance, especially at a high rotor speed, and the resulting damage (especially in the case of high-speed compressor stages), and it is thereby possible to avoid shifting of the co-rotating components relative to the axis of rotation of the compressor rotors or shifting of the axis of rotation of the rotating components, said shifting causing (operating) unbalance.
This applies especially also to co-rotating seal elements, especially also those of gas seals, the (co-rotating) masses of which can assume orders of magnitude which are relevant especially also to impeller masses.
Particularly in the case of gas seals with rotating seal elements, centering of the rotating seal elements is only possible through tight tolerances and/or additional centering elements, however. Moreover, it is generally impossible in that case to embody the connection between rotating seal elements and the carrier elements thereof without play, and therefore shifting of the axis of rotation of the rotating seal elements is possible to a limited extent (operating unbalance).